Endocrine cells in the gut of the shore crab Carcinus maenas immunoreactive to crustacean hyperglycaemic hormone and its precursor-related peptide

The distribution and morphology of gut endocrine cells, which are immunorea ctive to crustacean hy perglycaemic hormone (CHH) and the corresponding pre cursor-related peptide (CPRP), have been described in the shore crab Carcin us maenas. The cells are unique ly distributed throughout the fore- and hin dgut, but were never observed in the midgut or associated caeca. Expression of CHH and CPRP in the gut endocrine cells is generally restricted to prem oult, although small numbers of immunoreactive cells were observed in inter moult and postmoult. A notable feature of the distribution of these slender cells was that, whilst they are distributed evenly over much of the fore- and hindgut, all extrinsic and intrinsic muscles of the gastric and pyloric stomach examined were surrounded by a ring(s) of cells, suggesting a mecha noreceptive function. Ultrastructural studies revealed that these cells con tain numerous immunopositive, electron-dense granules. This suggests that t hey are "paraneurones", which secrete CHH and CPRP into the haemolymph duri ng ecdysis, accounting for the ecdysial surge in CHH, which is implicated i n water uptake and swelling prior to ecdysis.